The details depend on how you design your database to control navigation from layout to layout. You can, for example, hide and lock the tool bar (also called the status bar) in your onFirstWIndow open script and use scripted buttons or your own drop down list with script trigger to take a user to other layouts. If you use that interface design, all of these scripts can select the layout that is appropriate for the device in use by the current user.
You can also set up onLayoutEnter script triggers to check the device information and change layouts if needed to use one appropriate for the current device in use.
Once again, thanks for your help Phil. I do have the navigation buttons, I just thought maybe there was a script that would find the device, then apply only certain user privileges to limit the layouts. For example, when it finds an iPhone, it goes to the privileges that only allow iPhone layouts, etc.
I think I'll be retired by the time I finally get this database the way I (think) I want it.
Yes, but as far as I know, you can't where you can do it with the script. (Keep in mind that if you could do it and FileMaker Inc. implemented it like they do record level access (as opposed to layout access), you'd still be able to go to that layout, but you'd find it covered by a grey screen with the words "no access" where the script avoids taking the user to that layout in the first place.